This invention relates to a method of detecting a crank angle signal abnormality applicable to the electronic control unit of an internal combustion engine.
Control signals which accurately represent the crank angle position of the crankshaft of an internal combustion engine are used by an electronic control unit, such as a fuel injection control unit or ignition timing control unit, to control the operation of the engine. These control signals include a cylinder discriminating signal for specifying one of the plural cylinders of the engine, a reference position signal indicative of a predetermined crank angle position, e.g. top dead center (TDC) at the end of the compression stroke, which serves as a reference for controlling each cylinder, and an angle position signal generated whenever the crankshaft rotates through a predetermined angle to give an indication of the crank angle position.
An automotive vehicle having an internal combustion engine is equipped with a window wiper motor, an ignition system, a starter, warning devices and the like. If noise produced by these items of equipment when they are operated is superimposed on any of the three control signals mentioned above, difficulty is encountered in controlling the operation of the engine. This is particularly the case if noise is superimposed on the reference position signal or crank angle position signal, for any abnormality in these signals makes it difficult to determine an accurate ignition advance angle when controlling ignition timing. This can have an adverse upon the engine.